CORE Metadata, citation and similar papers at core.ac.uk Provided by ScholarSpace at University of Hawai'i at Manoa Cephalopods in the Diet of Swordfish (Xiphias gladius) Caught off the West Coast of Baja California, Mexico1 Unai Markaida2,3 and F. G. Hochberg4 Abstract: The lower beaks of 1,318 cephalopods from the stomach contents of 175 swordfish, Xiphias gladius, caught off the west coast of Baja California, Mexico, between 1988 and 1996 were analyzed. In total, 20 species of teuthoids, 4 octopods, and one vampyromorph were identified. Weights and lengths of cephalopods were estimated from the lower rostral lengths. Ommastrephid squids, primarily jumbo squid Dosidicus gigas of different maturing sizes, com- posed 60% by number and 82% by estimated weight. Three species of gonatids were identified and represented 22% by number. An unidentified species of Argonauta was the most abundant octopod, with 5.8% of the beak total. Ancis- trocheirus lesueurii is recorded for the first time in the California Current. Dis- tribution of cephalopods in the California Current and their size in the diet of other marine predators are discussed. The diet of swordfish was dominated by medium to large muscular squid species that probably are eaten in surface waters at night. Clarke (1966) noted that marine predators of these mollusks. Information on oceanic prey on species of cephalopods that often are cephalopods in the diet of marine predators poorly known. In fact, the study of cephalo- in the California Current and northeastern pod remains in the stomach contents of ma- Pacific Ocean has come principally from rine predators has contributed greatly to our studies on marine mammals, mainly odonto- knowledge of the distribution and ecology cetes or toothed whales and pinnipeds. Squids recovered from the stomach con- tents of sperm whales, Physeter macrocephalus 1 This paper resulted from parts of the M.S. thesis Linnaeus, 1758, from the Bering Sea and of U.M. Thesis work was supported by a multinational Gulf of Alaska were documented by Okutani grant from the Consejo Superior de Investigaciones and Nemoto (1964). Clarke and MacLeod Cientı´ficas (CSIC) in Spain and the Consejo Nacional de (1980) identified cephalopod remains from 20 Ciencia y Tecnologı´a (CONACyT) in Mexico. Manu- sperm whales caught off western Canada, and script accepted 9 March 2004. 2 Corresponding author. Fiscus et al. (1989) reported on beaks found 3 Departamento de Ecologı´a, Centro de Investiga- in 175 specimens of the same predator off cio´n Cientı´fica y de Educacio´n Superior de Ensenada California. Mead et al. (1982) analyzed beaks (CICESE), Ctra. Tijuana Ensenada km 107, Ensenada, from several Hubbs’ beaked whales, Meso- Baja California, Mexico. Current address: Departamento de Aprovechamiento y Manejo de Recursos Acua´ticos, El plodon carlhubbsi Moore, 1963, stranded in Colegio de la Frontera Sur, Unidad Campeche, Calle California and provided drawings of a pair of 10 Â 61, No. 264, Col. Centro, 24000 Campeche, Mexico Gonatus sp. beaks. Cephalopods found in a (phone: 52 981 816 4221 ext. 2406; fax: 52 981 816 5978 short-finned pilot whales, Globicephala macro- ext. 2102; e-mail: [email protected]). rhynchus Gray, 1846, salvaged off California 4 Department of Invertebrate Zoology, Santa Barbara Museum of Natural History, 2559 Puesta del Sol Road, were listed by Seagars and Henderson (1985) Santa Barbara, California 93105-2936 (phone: 805-682- and Hacker (1992). The beaks of an un- 4711 ext. 318; fax: 805-569-3170; e-mail: fghochberg@ identified gonatid squid collected from pilot sbnature2.org). whales are illustrated in Hacker (1992). Fiscus (1982) examined cephalopod re- Pacific Science (2005), vol. 59, no. 1:25–41 mains recovered from the northern fur seal, : 2005 by University of Hawai‘i Press Callorhinus ursinus (Linnaeus, 1758), and other All rights reserved marine mammals taken from California to the 25 26 PACIFIC SCIENCE . January 2005 Bering Sea. Cephalopods in the diets of the in 138 of those stomachs are treated here. An California sea lion, Zalophus californianus additional collection of 37 swordfish stom- (Lesson, 1828), and the northern elephant achs irregularly collected in the same area by seal, Mirounga angustirostris (Gill, 1866), off commercial fishermen from 1988 to 1996 southern California were discussed in reports also was analyzed. Prey quantification in these by Lowry and coworkers (1990, 1999), stomach contents was made as previously de- Hacker (1986), and Antonelis et al. (1994). scribed (Markaida and Sosa-Nishizaki 1998). Other works on the diet of marine predators Both collections of cephalopod lower beaks have only listed cephalopod prey. For teleosts were examined together in the study de- Galva´n-Magan˜ a et al. (1985) treated in detail scribed here. the cephalopods found in yellowfin tuna, Cephalopod beaks were identified utilizing Thunnus albacares (Bonnaterre, 1788), from keys in Iverson and Pinkas (1971), Wolff the California Current. (1984), Clarke (1986), and Fiscus (1991). Several guides are available that provide Identifications were checked against identi- illustrations useful for identification of the fied voucher samples in the collection of beaks of cephalopods found in predator the Department of Invertebrate Zoology, stomachs in the northeastern Pacific Ocean; Santa Barbara Museum of Natural History see especially Iverson and Pinkas (1971), (sbmnh), Santa Barbara, California. Vouchers Wolff (1984), and Fiscus (1991). of almost every cephalopod species identified The swordfish, Xiphias gladius Linnaeus, in the fauna of the eastern Pacific Ocean are 1758, is one of the largest teleost predators present in the collections of sbmnh. Two that is distributed, and commercially fished, beak samples were identified by Malcolm worldwide in temperate and tropical seas Clarke (pers. comm., January 1995). Rostral (Nakamura 1974). Swordfish also undertake lengths (LRL) or hood lengths (LHL) of daily vertical migrations (Carey and Robinson lower beaks were measured with a vernier 1981). These characteristics, coupled with the caliper or micrometer to 0.05 mm. Frequency fact that cephalopods account for a large per- histograms for the most numerous species centage of the diet of this predator, have were constructed from these measurements. encouraged studies on cephalopods from the Darkening of the wings of lower beaks was stomach contents of swordfish in various re- analyzed because it indicates the maturity gions of the world: northwestern Atlantic process in cephalopods (Mangold and Fioroni Ocean (Florida Straits: Hess and Toll 1981, 1966). In ommastrephids the presence of Toll and Hess 1981), eastern Mediterranean completely pigmented beak wings indicates Sea (Bello 1991), northeastern Atlantic Ocean sexual maturity (Herna´ndez-Garcı´a et al. (Guerra et al. 1993, Clarke et al. 1995, Her- 1998). Equations were available for certain na´ndez-Garcı´a 1995), and North-central cephalopod species that were used to estimate Pacific Ocean (Hawai‘i: Seki 1993). In this weights and mantle lengths (ML), based study we examined the cephalopod remains on measurements of LRLs or LHLs (Wolff collected from the stomach contents of 1984, Clarke 1986, Kubodera 1986, Smale et swordfish from the southern portion of the al. 1993). California Current, in the northeastern Pa- cific Ocean. results materials and methods Cephalopods dominated the diet of the swordfish in the 37 samples collected between The stomach contents of 173 swordfish 1988 and 1996. They occurred in all stom- caught off the west coast of Baja California, achs and represented 92% by number and Mexico, during 1992 and January 1993 were 76% by weight of all prey (Table 1). In total, analyzed in a swordfish food and feeding 1,318 lower beaks belonging to at least 25 habits study (Markaida and Sosa-Nishizaki cephalopod species (Table 2) were identified 1998). The lower beaks of cephalopods found pooling these and previous samples (Mar- Cephalopods in the Diet of Swordfish . Markaida and Hochberg 27 TABLE 1 Prey Species by Number, Weight, and Frequency of Occurrence in the Stomach Contents of 37 Swordfish Caught off the West Coast of Baja California during 1988–1996 Taxon Number % Weight (g) % Frequency % CEPHALOPODA 384 92.53 14,618 76.24 37 100.00 Dosidicus gigas (jumbo squid) 197 47.35 12,481 65.09 33 89.18 Sthenoteuthis oualaniensis (flying squid) 11 2.64 — — 7 18.91 Gonatus berryi 109 26.20 — — 23 62.16 ‘‘Gonatus californiensis’’ 3 0.72 112 0.58 2 5.40 Gonatopsis borealis 4 0.96 — — 3 8.10 Onychoteuthis cf. banksii 7 1.68 — — 6 16.21 Onychoteuthis borealijaponicus 2 0.48 — — 2 5.40 Unidentified onychoteuthid 30 7.21 — — 4 10.81 Ancistrocheirus lesueurii 6 1.44 520 2.71 4 10.81 Histioteuthis heteropsis 3 0.72 — — 3 8.10 Mastigoteuthis sp. 2 0.48 — — 2 5.40 Loligo opalescens (market squid) 2 0.48 — — 1 2.70 Thysanoteuthis rhombus 1 0.24 — — 1 2.70 Unidentified teuthoids 2 0.48 — — 2 5.40 Octopus rubescens 3 0.72 — — 1 2.70 Argonauta spp. (papershell) 2 0.48 — — 2 5.40 Cephalopoda remains — — 1,505 7.84 17 45.94 TELEOSTEI 31 7.45 4,554 23.75 15 40.54 Sardinops sagax (Pacific sardine) 9 2.16 396 2.06 4 10.81 Auxis spp. (frigate or bullet tuna) 8 1.92 2,731 14.24 6 16.21 Trachurus symmetricus (jack mackerel) 4 0.96 241 1.25 3 8.10 Scomber japonicus (Pacific mackerel) 3 0.72 106 0.55 2 5.40 Alepisaurus ferox (longnose lancetfish) 1 0.24 64 0.33 1 2.70 Unidentified scopelarchid 1 0.24 8 0.04 1 2.70 Merluccius productus (Pacific hake) 1 0.24 — — 1 2.70 Unidentified teleosts 5 1.20 1,006 5.24 5 13.51 Total 416 100.00 19,174 100.00 37 100.00 kaida and Sosa-Nishizaki 1998). The most made on the basis of the intrafamilial differ- important cephalopod families found in the ences in size and darkening of the beaks swordfish diet are treated here.